Smooth muscle cell (SMC) accumulation and extracellular matrix deposition in the intima are major characteristics of neointimal hyperplasia (IH) which occurs frequently following all forms of vascular reconstruction, including stenting, angioplasty, endarterectomy and vein grafts. A common result of IH is the reduction of the vessel lumen diameter leading to important clinical problems such as angina, stroke, thrombosis and myocardial infarction. It is our goal to identify biomarkers to assess risk of developing IH and molecular mediators for the development of therapies to treat susceptible vessels. Among mouse strains, there is a wide range of responses to carotid artery injury as induced by ligature, slow flow or endothelial denudation ranging from mice that are completely resistant those which develop large neointimal lesions. Here, we exploit these phenotypic differences by using genetic linkage and association studies to identify genes modulating vascular pathology in carotid arteries. Since the last submission, we have altered the emphasis of our outstanding research team to include family linkage and association study expertise. We also nearly doubled an F2 population between FVB (susceptible) and C57BL/6 (resistant) strains and identified 6 quantitative trait loci (QTL). An identity by descent analysis was performed across 10 inbred strains to reduce QTL intervals which yielded 8 candidate genes worthy of further study. We also screened 9 inbred mouse strains in anticipation of entering them into a large association study. We present validation data for one candidate gene and show its relevance to the IH process. Overall, we expect to use this unbiased system for the discovery of novel genes controlling IH. Work will be conducted as described in three Specific Aims: (1) Identify chromosomal intervals containing genes modulating susceptibility and resistance to injury-induced neointimal hyperplasia (IH). We will use classic linkage studies to identify QTL and haplotype analysis across F2 mice to eliminate regions that are shared identical by descent. (2) Identify genes and molecular pathways mediating responsiveness to carotid artery injury using genome wide association studies. We will use a mouse diversity panel of ~100 inbred strains for which genotypes are already known and obtain IH phenotypes for association studies. (3) Validate and determine functions for potential candidate genes controlling IH. Candidate genes discovered in Aims 1 and 2 will be studied further here. Such studies will include identification of cell type(s) involved in expression, characterization of molecular functions in cultured cells, and development of appropriate genetically engineered mice. Overall, the strengths of this proposal include: (a) the novelty of the topic; (b) outstanding research team; (c) currently existing QTL for IH; and (d) strong preliminary data identifying a candidate gene with potential IH-modulating activity which demonstrates the utility of our approach. Further, the health topic is of high significance as tens of thousands of individuals are affected by vascular injury each year.